The present invention relates generally to an inductor and, more particularly, to an inductor with multiple air gaps for thermal management.
High power motor controllers typically require inductors exhibiting stable inductance at both high magnitude currents and at frequencies ranging from DC to tens of kilohertz. Parameters for one such inductor, typical of aerospace applications, operates at: 35 μH rated for 260 A at 1,400 Hz continuous. An inductor designed to these parameters should retain 90% inductance at DC currents up to 880 amps. These inductors, specifically power quality filter inductors, should be lightweight and be configured for conduction cooling. Use in aerospace applications heightens the need for lightweight inductors.
Many conventional inductor permutations attempt to meet desired performance parameters yet minimize inductor weight. One such inductor is a gapped tape-wound cut core inductor. This type of inductor contains a magnetic core and typically exhibits high losses around the air gaps due to magnetic core eddy currents which are caused by flex fringing near the air gaps in the magnetic core. As a result, the heat generated by the inductor may most noticeably increase in the areas adjacent the air gaps. In addition, high temperatures may be realized in inductor portions proximate the air gaps. Air gaps in the magnetic path create a high reluctance path, avoiding saturation of the magnetic field at lower frequencies.
Powder magnetic core materials have been used in an attempt to reduce the high temperatures. The powder core materials inherently contain distributed air gaps, which minimize flux fringing and eddy current losses. However, as the DC magnetizing force of the inductor increases, the effective permeability of the powder core drops significantly which thereby limits the effectiveness of the powder magnetic core material to reduce inductor temperatures, especially in inductors producing high magnetizing forces.
Reducing the number of coil turns increases the current with which the permeability of the powder core drop becomes unacceptable. However, to maintain the desired inductance, the cross-sectional area of the powder core must increase substantially in response to a decrease in the number of coil turns, such that the overall weight of the inductor increases, with disadvantageous results for aerospace applications.
Other attempts to minimize the high temperatures generated by the inductors include eliminating entirely the ferromagnetic core. This approach results in an air core inductor with no air gaps or gap losses but requires a significant number of turns and relatively large diameter inductors coils to generate sufficient inductance. Eliminating the ferromagnetic core also induces high magnetic fields outside of the area enclosed by the coil windings, which may heat metal surfaces near the inductor and may interfere with the fields of other inductors in the area. Thus, the elimination of the ferromagnetic core results in a relatively large mounting footprint and stray magnetic fields, which may have disadvantageous results in aerospace applications.
Accordingly, it is desirable to provide an inductor for aerospace applications that minimizes eddy current losses and effectively facilitates inductor heat conduction.